can I ask you how your wall mount fits on the imac? I could not see a way for the arm of come off of them when I looked at them in the store.
There is a Vesa adapter that is made for the iMac.
This is it. Its quite simple actually. You lay the iMac face down, and tilt base as far down as it goes. Then you take this plastic card (size of a credit card), and slide it in where the base connects to the iMac, at an upward angle, and the piece that connects the base comes out and reveals the 8 screws that need to be removed. Once you get that done, the Vesa mount attaches quite easily, then you add it to any wall mount that is compatible with the Vesa mount, which are pretty much any wall mount available.
The tricky part is getting the wall mount on the wall straight lol. I put up my 42" tv with a friend of mine, and had to fix it a little because it was at a slight angle, which was hardly noticeable, except to me. I measured, and measured again, and again, until I was ready to do it. I did it myself, and was quite pleased when I checked the iMac afterward and it was perfectly leveled.
Next step is to upgrade the desk, or at least a new base for the glass.